Microbiota Signals Suppress the Lymphoid Specification of Hematopoietic Stem Cells

Aging is associated with an expansion of phenotypic hematopoietic stem cells (HSCs) with reduced self-renewal capacity and myeloid-skewed lineage differentiation. Signals from commensal flora support basal myelopoiesis in young mice; however, their contribution to hematopoietic aging is largely unknown. Here, we characterize hematopoiesis in young and middle-aged mice housed under specific pathogen free (SPF) and germ-free (GF) conditions. We did not analyze older mice due to the difficulty in maintaining mice in a gnotobiotic facility for more than one year. Consistent with prior studies, there is a shift in hematopoiesis in aged SPF mice towards granulopoiesis, with a significant increase in the percentage of granulocytic cells and a decrease in B lineage cells in the bone marrow. The marked shift from lymphopoiesis to myelopoiesis that develops during aging of SPF mice is mostly abrogated in GF mice. Compared with aged SFP mice, there is a marked expansion of B lymphopoiesis in aged GF mice, which is evident at the earliest stages of B cell development. To investigate the impact of microbiota signals on multipotent HSPCs, we first quantified HSPCs by flow cytometry (Figure 1A-B). In aged SPF mice, the number of lineage - Sca1 + cKit + CD150 + CD48 - (LSK-SLAM) cells and CD34 - LSK-SLAM cells is increased 6.4 ± 1.7-fold and 3.4 ± 1.2-fold, respectively. Similar increases were observed in aged GF mice, with LSK-SLAM increasing 5.3 ± 1.6-fold (p=NS compared to SPF mice) and CD34 - LSK-SLAM cells increasing 2.8 ± 0.31-fold (p=NS). To quantify functional HSCs, limiting dilution transplantation experiments using unsorted bone marrow cells was performed. Although on a per cell basis the repopulating activity of aged HSCs is reduced, due to the large increase in phenotypic HSCs, the number of functional HSCs actually increases with aging, with similar increases in functional HSCs in aged SPF and GF mice (Figure 1C). Finally, to assess lineage-bias, we transplanted a limiting number of sorted HSCs and assessed lineage output. As expected, in young SPF mice, the majority of HSCs displayed a balanced myeloid/lymphoid lineage output, with a significant increase in myeloid-biased HSCs observed with aging (Figure 1D). In young GF mice, the majority of HSCs are lymphoid-biased. Moreover, although the myeloid output increased modestly with aging, the majority of HSCs in aged GF remained lymphoid-biased or balanced. Consistent with these data, RNA expression profiling of phenotypic HSCs from aged GF mice show enrichment for non-myeloid biased HSCs. Surprisingly, the RNA expression profiling data also suggest that inflammatory signaling is increased in aged GF HSCs compared with aged SPF HSCs. Collectively, these data suggest that microbiota-related signals suppress the lymphoid potential of HSCs, contributing to the expansion of myeloid-biased HSCs that occurs with aging. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Microbiota Signals Suppress B Lymphopoiesis With Aging in Mice

Aging is associated with significant changes in hematopoiesis that include a shift from lymphopoiesis to myelopoiesis and an expansion of phenotypic hematopoietic stem cells (HSCs) with impaired self-renewal capacity and myeloid-skewed lineage differentiation. Signals from commensal flora support basal myelopoiesis in young mice; however, their contribution to hematopoietic aging is largely unknown. Here, we characterize hematopoiesis in young and middle-aged mice housed under specific pathogen free (SPF) and germ-free (GF) conditions. The marked shift from lymphopoiesis to myelopoiesis that develops during aging of SPF mice is mostly abrogated in GF mice. Compared with aged SPF mice, there is a marked expansion of B lymphopoiesis in aged GF mice, which is evident at the earliest stages of B cell development. The expansion of phenotypic and functional HSCs that occurs with aging is similar in SPF and GF mice. However, HSCs from young GF mice have increased lymphoid lineage output, and the aging-associated expansion of myeloid-biased HSCs is significantly attenuated in GF mice. Consistent with these data, RNA expression profiling of phenotypic HSCs from aged GF mice show enrichment for non-myeloid biased HSCs. Surprisingly, the RNA expression profiling data also suggest that inflammatory signaling is increased in aged GF HSCs compared with aged SPF HSCs. Collectively, these data suggest that microbiota-related signals suppress B lymphopoiesis at multiple stages of development and contribute to the expansion of myeloid-biased HSCs that occurs with aging.

The spliceosome factor sart3 regulates hematopoietic stem/progenitor cell development in zebrafish through the p53 pathway

Hematopoietic stem cells (HSCs) possess the potential for self-renew and the capacity, throughout life, to differentiate into all blood cell lineages. Yet, the mechanistic basis for HSC development remains largely unknown. In this study, we characterized a zebrafish smu471 mutant with hematopoietic stem/progenitor cell (HSPC) defects and found that sart3 was the causative gene. RNA expression profiling of the sart3smu471 mutant revealed spliceosome and p53 signaling pathway to be the most significantly enriched pathways in the sart3smu471 mutant. Knock down of p53 rescued HSPC development in the sart3smu471 mutant. Interestingly, the p53 inhibitor, mdm4, had undergone an alternative splicing event in the mutant. Restoration of mdm4 partially rescued HSPC deficiency. Thus, our data suggest that HSPC proliferation and maintenance require sart3 to ensure the correct splicing and expression of mdm4, so that the p53 pathway is properly inhibited to prevent definitive hematopoiesis failure. This study expands our knowledge of the regulatory mechanisms that impact HSPC development and sheds light on the mechanistic basis and potential therapeutic use of sart3 in spliceosome-mdm4-p53 related disorders.

JAK2V617F mutant megakaryocytes contribute to hematopoietic aging in a murine model of myeloproliferative neoplasm

Megakaryocytes (MKs) is an important component of the hematopoietic niche. Abnormal MK hyperplasia is a hallmark feature of myeloproliferative neoplasms (MPNs). The JAK2V617F mutation is present in hematopoietic cells in a majority of patients with MPNs. Using a murine model of MPN in which the human JAK2V617F gene is expressed specifically in the MK lineage, we show that the JAK2V617F-bearing MKs promote hematopoietic stem cell (HSC) aging, manifesting as myeloid-skewed hematopoiesis with an expansion of CD41+ HSCs, a reduced engraftment and self-renewal capacity, and a reduced differentiation capacity. HSCs from 2yr old mice with JAK2V617F-bearing MKs were more proliferative and less quiescent than HSCs from age-matched control mice. Examination of the marrow hematopoietic niche reveals that the JAK2V617F-bearing MKs not only have decreased direct interactions with hematopoietic stem/progenitor cells during aging, but also suppress the vascular niche function during aging. Unbiased RNA expression profiling reveals that HSC aging has a profound effect on MK transcriptomic profiles, while targeted cytokine array shows that the JAK2V617F-bearing MKs can alter the hematopoietic niche through increased levels of pro-inflammatory and anti-angiogenic factors. Therefore, as a hematopoietic niche cell, MKs represent an important connection between the extrinsic and intrinsic mechanisms for HSC aging.

Models that combine transcriptomic with spatial protein information exceed the predictive value for either single modality

Immunotherapy has reshaped the field of cancer therapeutics but the population that benefits are small in many tumor types, warranting a companion diagnostic test. While immunohistochemistry (IHC) for programmed death-ligand 1 (PD-L1) or mismatch repair (MMR) and polymerase chain reaction (PCR) for microsatellite instability (MSI) are the only approved companion diagnostics others are under consideration. An optimal companion diagnostic test might combine the spatial information of IHC with the quantitative information from RNA expression profiling. Here, we show proof of concept for combination of spatially resolved protein information acquired by the NanoString GeoMx® Digital Spatial Profiler (DSP) with transcriptomic information from bulk mRNA gene expression acquired using NanoString nCounter® PanCancer IO 360™ panel on the same cohort of immunotherapy treated melanoma patients to create predictive models associated with clinical outcomes. We show that the combination of mRNA and spatially defined protein information can predict clinical outcomes more accurately (AUC 0.97) than either of these factors alone.

Multiomic analysis to reveal distinct molecular profiles of uterine and nonuterine leiomyosarcoma.

11555 Background: Leiomyosarcoma (LMS) is a rare group of mesenchymal malignancies found in the uterus, retroperitoneum, skin, or other soft-tissue sites. Treatment for LMS is extrapolated from trials including both uterine (uLMS) and non-uLMS subtypes, although whether they respond similarly and have similar outcomes from treatment is not clear. We examined the molecular composition of LMS by site of origin to better inform future drug development and trial design. Methods: We reviewed 1115 specimens with LMS histology tested by Caris Life Sciences for targeted exome (NextSeq, 592 gene panel), whole exome, and whole transcriptome sequencing (NovaSeq). Specimens were stratified into uLMS, rpLMS (retroperitoneal), and otherLMS (non-uterine/retroperitoneal) subgroups based on tumor origin sites. Genomic data was analyzed for mutations, copy number aberrations, and fusions. RNA expression profiling included evaluation of individual genes and gene set enrichment analysis (GSEA). P-value adjustment performed by the Benjamini-Hochberg procedure. Results: The study cohort was comprised of 62.9% uLMS (n = 701), 14.9% rpLMS (n = 166) and 22.2% otherLMS (n = 248) specimens. Overall, LMS specimens most frequently harbored TP53 (64%, n = 612), ATRX (30%, n = 219), RB1 (22%, n = 156), and MED12 (16%, n = 94) mutations, with these genes accounting for 74.4% (n = 1044) of all observed pathogenic/likely pathogenic mutations. RB1 mutations were significantly less common in uLMS (15%) compared to rpLMS (30%, p < 0.05) and otherLMS (33%, p < 0.01), whereas MED12 mutations were almost exclusive to uLMS (22% vs 1% rpLMS, 3% otherLMS, p < 0.05). MAP2K4 copy number amplification were more common in rpLMS (22%, p < 0.001) and otherLMS (14%, p < 0.182) compared to uLMS (7%), with frequent co-amplification of nearby genes ( FLCN, GID4, SPECC1, GAS7, PER1, and AURKB) located at chr17p11-13. Actionable gene fusions involving ALK (2.1%, n = 11), FGFR1 (0.2%, n = 1), and NTRK1/2 (0.2%, n = 1 each) were rare overall, with similar prevalence across subtypes. Genomic alteration rates were not significantly different between rpLMS and otherLMS subtypes . RNA expression profiling identified significant upregulation of PI3K/AKT/mTOR, DDR, WNT/Beta-Catenin pathway genes in non-uLMS. GSEA indicated several immune-related gene sets were enriched in rpLMS and otherLMS compared to uLMS. Conclusions: Comprehensive molecular profiling suggests that LMS originating from the uterus represents a molecularly distinct disease compared to other primary sites of origin. We identified key genomic patterns which have potential for targeted therapy. These data provide insight for the framework of future clinical trials designed to separate uLMS from non-uLMS histologies, although further subdivision does not appear to be warranted.

JAK2-V617F and interferon-α induce megakaryocyte-biased stem cells characterized by decreased long-term functionality

We studied a subset of hematopoietic stem cells (HSCs) that are defined by elevated expression of CD41 (CD41hi) and showed bias for differentiation toward megakaryocytes (Mks). Mouse models of myeloproliferative neoplasms (MPNs) expressing JAK2-V617F (VF) displayed increased frequencies and percentages of the CD41hi vs CD41lo HSCs compared with wild-type controls. An increase in CD41hi HSCs that correlated with JAK2-V617F mutant allele burden was also found in bone marrow from patients with MPN. CD41hi HSCs produced a higher number of Mk-colonies of HSCs in single-cell cultures in vitro, but showed reduced long-term reconstitution potential compared with CD41lo HSCs in competitive transplantations in vivo. RNA expression profiling showed an upregulated cell cycle, Myc, and oxidative phosphorylation gene signatures in CD41hi HSCs, whereas CD41lo HSCs showed higher gene expression of interferon and the JAK/STAT and TNFα/NFκB signaling pathways. Higher cell cycle activity and elevated levels of reactive oxygen species were confirmed in CD41hi HSCs by flow cytometry. Expression of Epcr, a marker for quiescent HSCs inversely correlated with expression of CD41 in mice, but did not show such reciprocal expression pattern in patients with MPN. Treatment with interferon-α further increased the frequency and percentage of CD41hi HSCs and reduced the number of JAK2-V617F+ HSCs in mice and patients with MPN. The shift toward the CD41hi subset of HSCs by interferon-α provides a possible mechanism of how interferon-α preferentially targets the JAK2 mutant clone.

A venous-specific purinergic signaling cascade initiated by Pannexin 1 regulates TNFα-induced increases in endothelial permeability

The endothelial cell barrier regulates the passage of fluid between the bloodstream and underlying tissues, and barrier function impairment exacerbates the severity of inflammatory insults. To understand how inflammation alters vessel permeability, we studied the effects of the proinflammatory cytokine TNFα on transendothelial permeability and electrophysiology in ex vivo murine veins and arteries. We found that TNFα specifically decreased the barrier function of venous endothelium without affecting that of arterial endothelium. On the basis of RNA expression profiling and protein analysis, we found that claudin-11 (CLDN11) was the predominant claudin in venous endothelial cells and that there was little, if any, CLDN11 in arterial endothelial cells. Consistent with a difference in claudin composition, TNFα increased the permselectivity of Cl− over Na+ in venous but not arterial endothelium. The vein-specific effects of TNFα also required the activation of Pannexin 1 (Panx1) channels and the CD39-mediated hydrolysis of ATP to adenosine, which subsequently stimulated A2A adenosine receptors. Moreover, the increase in vein permeability required the activation of the Ca2+ channel TRPV4 downstream of Panx1 activation. Panx1-deficient mice resisted the pathologic effects of sepsis induced by cecal ligation and puncture on life span and lung vascular permeability. These data provide a targetable pathway with the potential to promote vein barrier function and prevent the deleterious effects of vascular leak in response to inflammation.